This disclosure generally relates to motion capture systems for tracking the position and orientation of non-destructive inspection (NDI) sensor units designed to scan a target area.
In NDI applications, one of the problems to overcome is achieving accurate location (position and orientation) tracking, particularly for applications beyond a simple X-Y grid. Motion capture systems are commercially available which can be used to address this problem using very accurate (sub-millimeter) position tracking.
Existing NDI tracking solutions typically use direct encoder input, such as a wheeled rotary encoder connected directly to the NDI scanning hardware. For example, a one-dimensional scanning unit is known that uses an integrated wheeled encoder, where the motion of the wheel over the surface provides distance traveled for processing by the NDI scan application. This type of configuration works fine if the operator can maintain a straight motion path, the encoder wheel does not slip, and there are no discontinuities in the surface. But there are many applications in which the area to be scanned does not fit well with standard encoder-based tracking process, including motion paths requiring more of a free-form motion over surfaces. These surfaces may have obstructions that will cause the encoder wheel to skip, which causes a disruption in the alignment of the recorded scan. In addition, standard encoder-based tracking can only provide relative motion tracking, which gives a dead-reckoning type of solution based on the initial starting position; in accordance with that process, any wheel disturbances lead to accumulating positioning error. Typical encoder-based implementations do not address orientation of the NDI sensor array relative to the scanned object, which leads to scan misalignment and is another source of accumulating error.
Another type of existing tracking apparatus used for NDI scanning is an X-Y track type of device. This type of system is attached to the object to be scanned and uses direct input of X and Y linear encoder data to the NDI scanning hardware. This type of device does not suffer from drift, but requires extra space on the surface of the scanned object in which to install the X-Y track elements.
Another type of tracking device allows for two-dimensional motions, but this device only allows motion of one axis at a time. The user is required to press a button to switch the direction of motion. Since it is encoder-based, it can only measure relative motion and is susceptible to drift.
There is a need for a system that enables precise tracking of the position and orientation of a NDI sensor unit and conversion of the acquired tracking data into encoder pulse signals for processing by a NDI scanning system.